The lobster's stomatogastric ganglion drives the gastric mill with a centrally generated motor pattern. The synaptic network formed by the gastric neurons in the ganglion is known. I think this synaptic network combines with postinhibitory rebound in individual cells and synaptic facilitation and depression at particular synapses to determine both the firing order of each neuron in each cycle of the motor pattern and the repetition rate of the pattern. I want to test this hypothesis by: a. reversibly blocking all chemical synaptic transmission with high external Mg ions and low external Ca ions to see if patterned firing requires chemical synaptic transmission. b. interfering systematically with the firing of identified neurons during spontaneous activity to see if the altered pattern is consistent with the known synaptic network. c. filling pairs of identified neurons with procion yellow to see if their structures conform to the predictions made by the known network of synaptic connections. d. analysing the dynamics of the network with a digital model. Several gastric neurons have functional interactions which are not known to be direct or monosynaptic. I will investigate these possible connections by injecting TEA into the putative presynaptic neuron to see if its prolonged action potentials cause visible PSP's in the postsynaptic neuron, and by recording from identified sites in the integrative processes of these identified neurons to see if PSP's not detectable at the soma can be discovered closer to the spike-initiating zone. The synaptic organization of the gastric system has several dynamic characteristics which contribute to the motor pattern. I will analyse them by: a. measuring the facilitation or depression which occurs at each chemical synapse. b. measuring any change in the electrotonic coupling between particular neurons which may occur because of chemical synaptic input. c. recording from the integrative segments of certain neurons the changes in membrane potential associated with gating of their impulses.